For full details on trackables, visit the OC Wiki at http://wiki.opencaching.us/index.php/Trackables.
GeoKrety means "Geo Mole" in Polish. GeoKret is singular, GeoKrety is plural.
The tracking web site for Geo Moles is http://geokrety.org/
Accounts are free on the site but an account is not needed to log Geo Moles in and out.
To use the site, just provide a trackable item and tag it with the site URL and a tracking code.